1. Field of the Invention
The present invention relates to a retracting tensioning mechanism for dispensing an elongated member, and more particularly to arrangements for supplying lengths of yarn from creels to a loom for purposes of weaving a fabric.
2. History of the Prior Art
Certain mechanisms and processes sometimes require that an elongated member be unwound from a carrier tube, bobbin or similar device under tension. It may be desirable or necessary in such operations that the tension on the elongated member be maintained relatively constant or at least within a relatively small range of values in the face of widely varying amounts of force exerted on the elongated member as it is unwound from the carrier tube. It may furthermore by desirable or necessary that the elongated member be retracted to some extent when the force thereon is sufficiently low and the elongated member becomes slack.
Examples of such arrangements and processes are found in the field of weaving. Certain types of weaving require relatively close control of tension on the yarns being fed into a loom so that a desired density, uniformity, precise alignment and other characteristics of the woven fabric can be achieved. This is particularly true in the case of woven fabrics used in the aerospace industry were requirements are usually far greater than in the general textile industry. Because of tension variations including periods of actual slack created by the movement of the harnesses in the loom to which the various warp yarns are fed, various different arrangements and techniques have been employed for supplying a plurality of warp yarns to the loom in a manner which attempts to minimize tension variations in the yarns. One such technique is used in conjunction with winding the individual dual yarns on a large drum or beam such that the individual yarns are wound side-by-side and under controlled tension. In weaving, the yarns feeding into the loom from the beam pass over whip rolls which serve to take up yarn slack and to maintain yarn tension during the shedding action of the loom harnesses. This has proven to be a relativley satisfactory technique in the case of nonfragile yarns such as those made of cotton, wool and synthetics such as nylon, rayon and the like. Such yarns are comprised of individual filaments which are twisted together before the yarn is wound on the drum or beam. Such yarns are relatively durable and are resistant to abrasion during handling and during the process in which the yarns are fed into the loom. The process of winding the yarns onto the drum or beam arrangement and thereafter dispensing the yarns in such a way that the yarns are required to undergo sharp bends therein and over relatively rough and abrasive surfaces does not pose a particular problem with twisted yarns of relatively durable composition.
A different set of considerations exist however where the fabric is being woven from relatively frgaile yarns such as those of graphite, ceramic or quartz composition. Such yarns may consist of a bundle of very fine filaments combined into a ribbon having little or no twist. The individual filaments have very little resistance to bending around a short radius and little resistance to abrasion. As sharp bends and abrasions occur, the individual filaments break and become trapped under adjoining ends, making it difficult to deliver the yarns into the loom and to weave a uniform fabric. The broken filaments tend to tangle, for example, making it difficult and in some cases impossible to feed the yarns through eyelets or other confined areas as the yarns are delivered to the loom.
Because of these problems, yarns of graphite or similar fragile composition are normally supplied to the loom using warp creels. Such arrangements dispose a plurality of yarn carrier tubes in rotatable, side-by-side relation so that the individual lengths of yarn wound on each carrier tube can be unwound from the tubes simultaneously for delivery into the loom. A friction-type element may be employed to bear against the carrier tubes or yarns to provide tension in the yarns. Alternatively, hairpin-shaped weights may be hung over the individual yarns in the regions where they are unwound from the carrier tube to apply tension to the yarns. As the warp harnesses in the loom are raised and lowered so as to create a condition of varying tension on the yarns, the hairpin-shaped weights have the effect of taking up some of the slack so as to reduce the effects of the tension variations. Nevertheless, even where the weights are used, the tension variations and inconsistencies are still too great in many instances for the satisfactory weaving of a precise, uniform fabric. In addition, the weights themselves involve additional bending and abrasion of the delicate yarns resulting in filament breakage, twisting and gathering.
Consequently, it is desirable in certain applications to utilize a tensioning arrangement which does not utilize suspended weights or similar devices having the attendant disadvantages noted above. Examples of arrangements for tensioning yarn or wire filaments are provided by U.S. Pat. Nos. 3,307,805 of Verbeek and B506,167 of Brown. Still other examples of tensioning devices using a type of rachet mechanism are provided by U.S. Pat. Nos. 3,314,623 of Blandino and 1,050,047 of Walkup. Still further examples of such arrangements are provided by U.S. Pat. Nos. 1,730,431 of Keefer and 1,914,014 of Gobeille. While such arrangements can function to provide some tension during the unwinding of an elongated web member, they tend to suffer from a number of shortcomings. Aside from mechanical complexity in some instances, such arrangements do not provide retraction of the web member under slack conditions while minimizing yarn damage in a simple and cost effective way. Moreover, the weaving of certain fabrics requires retraction of part or all of the warp during weaving.
Thus, while some variation of tension in the warp yarns is permissible in weaving operations of this type, it is important that a slack condition be prevented. Relatively constant tension under all conditions is nevertheless desirable, particularly if it can be accomplished without damgaging the fragile yarns. Accordingly, it is an object of the invention to provide an improved arrangement for maintaining tension in an elongated member.
If is a further object of the invention to provide an arrangement for maintaining in an elongated member tension which is relatively constant or at least within an acceptable range of values in the face of substantially widely varying amounts of force on the elongated member as it is being unwound from a carrier tube, bobbin or similar device.
It is a still further object of the invention to provide an arrangement for tensioning an elongated member, which arrangement is capable of retracting the elongated member during conditions of slack in the elongated member.